Răspuns:
Explicație pas cu pas:
2*3/5= 3/5+3/5=6/5
3*2/5= 2/5+2/5+2/5=6/5
2*7/5= 7/5+7/5=14/5
...
20*7/25= 7/25+7/25=...+7/ 25 de 20 ori= 140/25=28/5
sau
20*7/25= simplificam cu 5 = 4*7/5=7/5+7/5+7/5+7/5= 28/25
1/36*21= 21*1/36= 1/36+1/36+...+1/36 de 21 de ori =21/36= 7/12
sau
1/36*21=simplificam cu 3=1/12*7=7*1/12= 1/12+1/12+..+1/12 de 7 ori =7/12
